Variable pressure control valve

ABSTRACT

A variable pressure control valve arranged to enable a pilot piston having a comparatively small diameter to be used thereby making the whole body of the valve compact. This variable pressure control valve comprises a spool (2) kept in pressure contact with the valve seat of a pressurized fluid inlet port (1) by the resilient force of a compression spring (3); a stationary valve shoe (5) fixed so as to support the base end of the compression spring; and an auxiliary compression spring (6) which urges the spool (2) to the side of the valve seat on one side thereof and is urged by a pilot piston (4) on the other side thereof.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a variable pressure control valve arranged toenable the pressure of hydraulic fluid flowing thereinto from apressurized fluid inlet port to be variably set by introducing a pilotfluid pressure.

BACKGROUND ART OF THE INVENTION

As a variable pressure control valve, a valve constructed as shown, forexample, in FIG. 1 is known.

Stated briefly, a variable pressure control valve is known wherein aspool 2 is kept in pressure contact with a valve seat of a pressurizedfluid inlet port 1 by the resilient force of a compression spring 3, anda pilot fluid pressure Pp is introduced into a pilot piston 4 whichsupports the spring 3. The arrangement is made such that the forceexerted on the spool 2 to keep it in pressure contact with the valveseat of the pressurized fluid inlet port 1 is increased or decreased byvarying the pilot pressure Pp so that pressure of hydraulic fluidflowing thereinto from the pressurized fluid inlet port 1 can bevariably set.

In such a variable pressure control valve, since the compression spring3 is directly compressed by the pilot piston 4, it is necessary for thepilot piston 4 to have a large pressure receiving area. This results ina larger overall size of the valve, the valve cannot be made compact.

Stated more specifically, since in such a variable pressure controlvalve, the compression spring 3 having a high compression spring load iscompressed directly by the pilot piston 4 and the pilot pressure Ppexerted on the pilot piston 4 is generally 30 kg/cm², the pressurereceiving area of the pilot piston 4 needs to be increased in order toincrease the urging force thereof. Thus, the diameter of the pilotpiston 4 becomes larger, thus unavoidably making the overall size of thevalve larger.

Stating concretely, if the diameter of the pressurized fluid inlet port1 is designated by d, and the diameter of the pilot piston 4 by D₁, thenthe spring load W₁ set by the compression spring 3 is given by thefollowing formula ##EQU1## wherein P denotes the pressure within thepressurized fluid inlet port.

To increase the pressure P set in this condition by P, it is required toset the spring load W₁ at π/4d² (P+ΔP).

Further, the urging or pushing force F given by the pilot piston 4 willbe π/4D₁ ² X Pp.

Therefore, the diameter D₁ of the pilot piston 4 needs to be set at sucha value which enables the valve to support the above-mentioned springload W₁.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedcircumstances in the prior art and has for its object to provide avariable pressure control valve constructed to enable a pilot pistonhaving a comparatively small diameter to be used thereby making thewhole body of the valve compact to solve the above-mentioned problem inthe prior art.

To achieve the above-mentioned object, according to the presentinvention, there is provided a variable pressure control valvecomprising: a spool kept into pressure contact with the valve seat of apressurized fluid inlet port by the resilient force of a compressionspring; a stationary spring shoe fixed so as to support the base end ofthe compression spring; and an auxiliary compression spring which urgesthe above-mentioned spool to the side of the valve seat on one sidethereof and is urged by a pilot piston on the other side thereof.

According to the present invention having the above-mentioned aspect,since it is only necessary that the auxiliary compression spring isurged by a force which corresponds in magnitude to an increment inpressure to be set by the pilot piston, the urging force of the pilotpiston can be reduced so that the pressure receiving area of the pilotpiston can be reduced correspondingly.

Accordingly, the diameter of the pilot piston can be made comparativelysmall so that the whole body of the variable pressure control valve canbe made compact.

The above-mentioned and other objects, aspects and advantages of thepresent invention will become apparent to those skilled in the art bymaking reference to the following detailed description and theaccompanying drawing in which a preferred embodiment incorporating theprinciples of the present invention is shown by way of example only.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a prior art variable pressure control valve.

The present invention will now be described below by way of example onlywith reference to an embodiment shown in FIG. 2.

The variable pressure control valve according to the present inventionis constructed such that, as shown in FIG. 2, a compression spring 3 isinterposed between one end of a stationary or fixed spring shoe 5 andthe base end of a spool 2, and an auxiliary compression spring 6 havinga small compression spring load is interposed between the base end ofthe spool 2 and the leading end of a pilot piston 4 so that theauxiliary compression spring 6 can be compressed by the urging force ofthe pilot piston 4.

By such a construction, since the compression spring 3 having a highcompression spring load is supported by the stationary spring shoe 5,and the auxiliary compression spring 6 having a low compression springload is compressed by the urging force of the pilot piston 4 so that thepressure of hydraulic fluid flowing thereinto from a pressurized fluidinlet port 1 can be set at a high value, the urging force F provided bythe pilot piston 4 can be reduced to thereby enable the pressurereceiving area of the pilot piston 4. Hence, the diameter thereof isreduced.

Stated concretely, to increase the above-mentioned setting pressure byΔP, it is only necessary to set the compression spring load W₂ of theauxiliary compression spring 6 as follows. ##EQU2##

Wherein the urging force F of the pilot piston 4 is equal to π/4D₂ ² XPp.

Since the compression spring load W₂ is balanced with the urging forceF, ##EQU3##

Thus, the relationship between the diameter D₂ of the pilot piston 4 andthe diameter D₁ of the prior art pilot piston 4 will be ##EQU4##

Therefore, the diameter of the pilot piston 4 can be reduced.

The foregoing description is merely an example of preferred embodimentsof the present invention, and the scope of the present invention is notlimited to this example. Many changes and modifications of the presentinvention will readily occur to those skilled in the art withoutdeparting from the scope of the present invention.

What is claimed is:
 1. A variable pressure control valve comprising:aspool kept in a pressure contact with a valve seat of a pressurizedfluid inlet port by the resilient force of a compression spring whichprovides a first spring force urging said spool to a closed positionagainst a pressure of a fluid at said pressurized fluid inlet port: astationary spring shoe fixed so as to support a base end of saidcompression spring; and an auxiliary compression spring which urges saidspool to the side of said valve seat on one side thereof with a forcewhich is variable depending upon a position of a pilot piston having asmaller diameter than said stationary spring shoe and movable inresponse to a pilot pressure exerted on the end remote from saidauxiliary compression spring, said auxiliary compression spring exertinga second spring force variable depending upon the position of said pilotpiston for determining a set force for said spool in cooperation withsaid first spring force.
 2. A variable pressure control valve foropenably closing a pressurized fluid inlet port in a hydraulic passagesystem and for variably setting the force to close the port,comprising:a valve spool disposed for movement relative to saidpressurized fluid inlet port for selectively opening and closing saidinlet port depending upon the pressure of a fluid at said inlet port; afirst coil spring seated on said valve spool at one end and on astationary spring seat member at the other end for exerting a constantprimary spring force to said valve spool for providing a first set forcefor said valve spool, said stationary spring seat member being formedinto a cylindrical configuration defining a bore; a pilot pistondisposed in said bore of said stationary spring seat member for axialmovement toward any away from said valve spool and responsive to a pilotpressure exerted on a first end remote from said valve spool for axialmovement relative to said valve spool, said pilot piston having a secondend opposite to said first end; and a second coil spring coaxiallyarranged with said first coil spring and seated on said valve spool atone end and on said second end of said pilot piston for exerting anauxiliary spring force variable depending upon the axial position ofsaid pilot piston for providing a second set force for said valve spool,said second set force being cooperative with said first set force fordetermining the set force on said valve spool.
 3. A variable pressurecontrol valve for openably closing a pressurized fluid inlet port in ahydraulic passage system, comprising:a valve spool disposed for movementrelative to said pressurized film inlet port for selectively opening andclosing said inlet port depending upon the pressure of a fluid at saidinlet port; a first mechanical spring means seated on said valve spoolat one end and on a stationary spring seat member at the other end forexerting a primary spring force to said valve spool for providing afirst set force for said valve spool; a pilot piston disposed for axialmovement toward and way from said valve spool and responsive to a pilotpressure exerted on a first end remote from said valve spool for axialmovement relative to said valve spool, said pilot piston having a secondend opposite to said first end; a second mechanical spring means seatedon said valve spool at one end on said second end of said pilot pistonfor exerting an auxiliary spring force variable depending upon the axialposition of said pilot piston for providing a second set force for saidvalve spool, said second set force being cooperative with said first setforce for determining the set force on said valve spool; and saidstationary spring seat member being formed into a cylindricalconfiguration defining a bore slidably receiving said pilot piston.